Covariance and climate signals among state-of-the-art tree-ring proxies

Abstract

Tree-ring stable isotopes and wood anatomical traits emerged as powerful proxies for paleoclimate reconstructions, providing information beyond traditional ring width and wood density chronologies. However, comprehensive comparisons of these state-of-the-art tree-ring proxies derived from the same trees have yet to be performed to identify and differentiate their full paleoclimatic skill. Here, we assess covariance and climate signals in tree-ring width (TRW), maximum latewood density (MXD), cellulose stable carbon (δ¹³C_c) and oxygen (δ¹⁸O_c) isotopes, lignin methoxy carbon (δ¹³C_m) and hydrogen (δ²H_m) isotopes, radial cell lumen diameter (D_rad), and radial and tangential cell wall thickness (CWT_rad/CWT_tan) of ten Bosnian pines (Pinus heldreichii) from a treeline site on Mt. Smolikas, Greece. Proxy cross-comparison over the period 1861–2020 CE reveals strong covariance between detrended δ¹³C_c and δ¹³C_m (r ≥ 0.81). δ¹³C_c and δ¹⁸O_c exhibit the highest inter-series correlations (r ≥ 0.61) among all proxies. δ¹³C_c, δ¹³C_m, δ¹⁸O_c, together with D_rad, show considerable skill for reconstructing summer precipitation, whereas MXD and δ²H_m may be used for summer temperature reconstructions. Enhanced inter-series and hydroclimate correlations, along with a prolonged seasonality are significant advances of the isotopic and wood anatomical measurements compared to TRW. Our findings highlight the importance of integrating new isotopic, particularly δ¹³C_c, and xylem anatomical data into existing TRW networks to enhance our understanding of past hydroclimate variability and contextualize the recent aridification of the Mediterranean region.